It has been known for a longer time that chips produced in machining processes are ionized by frictional electricity during the machining process. While metallic chips often come into contact with the environment and/or with non-adjacent chips and discharge in this way, this does not hold true for chips made of materials which are not electrically conducting such as glass, ceramic or plastic materials. However, ionization is also observed when materials are machined which are poor conductors such as wood or graphite-reinforced plastics, that is to say plastic materials with embedded electrical conductors.
In order to improve the removal of chips it has become known to equip an air-pressure hose with an electrode which surrounds the aperture of the hose internally and extends around a drill which machines the non-conducting or poorly conducting material. In contrast, the provision of a simple electrode in the hose is considered to be less effective.
A disadvantage of the known solution is that by providing the spiral electrode the change of drills is influenced strongly. In order to improve effectiveness a high voltage of about 15 kV is provided with such a solution.
A solution of this type can be taken from U.S. Pat. No. 5,667,565, for instance.
However, the provision of such a high voltage is dangerous particularly when tools are changed such that it is not surprising that this solution which was intended particularly for air-craft construction has not become established.
Further numerous attempts have become known to improve the removal of chips which are produced by drills or other cutting tools.
In this connection it has been suggested to separate the ionization process of the supplied air from the actual supply and, in this context, to ensure deionization of the chips with ionized indoor air. However, it has become evident that a very high air-handling capacity is necessary for this purpose which makes the realization considerably more expensive and which is in particular also noisy.
Further, it has already been suggested to replace the voltage used for ionizing the air by a particular ac voltage to reduce the required voltage to values which are not dangerous.
However, particularly with strongly electrically insulating materials such as PMMA deposits of chips often remain at the workpiece or the workpiece holder, or in or at the space surrounding these parts.
The document JP S62 284731 A1 discloses a method for removing the frictional electricity in a mechanical processing system and for preventing the chips from adhering to the remaining components.
DE 10 2013 005 871 A1 discloses a numerically controlled machining center, in particular a multi-axis drilling and milling center, comprising a multi-axis drilling and milling device having a vertical spindle.
CN104 096 696 A discloses a method and a device for machining a blank and for collecting the resulting chips.